Results of the first interim assessment of rEECur, an international randomized controlled trial of chemotherapy for the treatment of recurrent and primary refractory Ewing sarcoma.

11007 Background: 5-year survival of RR-ES is about 15%. Several chemotherapy regimens are used, but without robust evidence. rEECur, the first randomised controlled trial in this setting, is defining a standard of care, balancing efficacy and toxicity. Methods: Patients aged 4 to 50 with RR-ES and fit to receive chemotherapy were randomised 2, 3 or 4 ways between topotecan & cyclophosphamide (TC), irinotecan & temolozomide (IT), gemcitabine & docetaxel (GD) or high-dose ifosfamide (IFOS). Primary outcome measure was objective response (OR) after 4 cycles by RECIST 1.1. Secondary outcomes included PFS, OS and toxicity. A probability-based Bayesian approach was used. The first interim assessment to determine which arm should be closed occurred when 50 evaluable patients had been recruited to 3 arms and evaluated for the primary outcome measure. Results: 242 patients (89% RECIST-evaluable) recruited between 18/12/14 and 21/06/18 were randomised to TC (n=75), IT (71), GD (66) and IFOS (30). Median age was 21 years (range 4 to 49). Patients had: refractory ES (20%), 1st recurrence (63%), >1st recurrence (17%); initial primary disease arose in bone in 60%; disease progression sites were primary site (17%), pleuropulmonary (29%) or other metastatic (54%). Median follow up was 11.3 months. Outcomes in the GD arm were: response rate 11.5% (95% CI: 4.4 to 23%), median PFS 3.0 months (95% CI: 1.6 to 8.0), median OS 13.7 months (95% CI: 10.1 to 23.9). The table shows, for each pairwise comparison of GD with the other arms (randomly labelled A, B, C to maintain blinding of open arms), the probabilities given the observed data that OR, PFS and OS were better for GD than for each other arm (RR: relative risk, HR: hazard ratio). For OR and PFS, all comparisons favoured the other arms. There were fewer grade 3/4 adverse events with GD than with the other arms pooled (58% v. 74%). Conclusions: rEECur has shown that GD is a less effective treatment than TC, IT or IFOS in reducing tumour burden or prolonging PFS in RR-ES. Recruitment continues to the remaining arms. Clinical trial information: ISRCTN36453794. [Table: see text]